1. Field of the Invention
The present invention relates to a detected method, and more particularly, to a target tracking method of radar with a frequency modulated continuous wave, which is used for increasing the radar target tracking efficiency.
2. Description of the Prior Art
Today, wireless communication technology is very developed. The radar's applications are very mature technology and particularly apply to a target tracking purpose. In the prior art, the waveform of the detected signal and reflected signal with the equal relative velocity between the radar with frequency modulated continuous wave and target is shown in FIG. 1. The type of the radar with frequency modulated continuous wave utilizes the radar transmitting a transmitted signal St. In a frequency sweep time T, the transmitted signal St is an upsweep frequency signal and the frequency of the transmitted signal St is increased from first frequency F1 to second frequency F2. Then, in next frequency sweep time T, the transmitted signal St is decreased from second frequency F2 to first frequency F1 so that the transmitted signal St can sweep up and sweep down periodically. The transmitted signal St is reflected from the target and then transmits on to the radar to form a reflected signal Sr.
The timing offset of the transmitted signal St and the reflected signal Sr is a delay time td, which is decided to the relative distance between the target and radar. When the radar is basis of the upsweep frequency signal being carried out to sweep, the delay time td causes the beat frequency fb1, the frequency offset of the transmitted signal St and the reflected signal Sr. When the radar is basis of the downsweep frequency signal being carried out to sweep, the delay time td causes the beat frequency fb2, the frequency offset of the transmitted signal St and the reflected signal Sr. If the beat frequency fb1 is equal to the beat frequency fb2 that means the relative velocity of the radar and the target is zero, so the relative frequency shift is not generated between the transmitted signal St and the reflected signal Sr. The distance between the radar and the target is calculated by range frequency fr, (fr=fb1=fb2), If the relative frequency shift is generated between the transmitted signal St and the reflected signal Sr that is a Doppler frequency shift fd. A relative velocity exists between the radar and target that is shown in FIG. 2 and FIG. 3.
In the prior art, the waveform of the transmitting signal and the reflected signal of the target approaching radar by constant speed is shown in FIG. 2. When the target approaches the radar by a constant speed, the Doppler frequency shift fd is generated between the transmitted signal St and the reflected signal Sr that will cause the beat frequency fb1 to reduce and cause the beat frequency fb2 to increase. In the prior art, the waveform of detected signal and reflected signal of the target leaving the radar by constant speed is shown as FIG. 3. When the target leaves the radar by constant speed, the Doppler frequency shift fd is generated between the transmitted signal St and the reflected signal Sr that will cause the beat frequency fb1 to increase and the beat frequency fb2 to reduce. The range frequency fr and the Doppler frequency shift fd are calculated by the radar getting the beat frequency fb1 and the beat frequency fb2. Then, the relative distance R of the target is got by the distance frequency fr and the target speed V is got by the Doppler frequency shift fd. The operation formula is as following description:
                              fb          ⁢                                          ⁢          1                =                  fr          -          fd                                    (        1        )                                          fb          ⁢                                          ⁢          2                =                  fr          +          fd                                    (        2        )                                fr        =                                            fb              ⁢                                                          ⁢              1                        +                          fb              ⁢                                                          ⁢              2                                2                                    (        3        )                                fd        =                                            fb              ⁢                                                          ⁢              2                        -                          fb              ⁢                                                          ⁢              1                                2                                    (        4        )                                R        =                              c            ×            T            ×            fr                                2            ×            Fs                                              (        5        )                                V        =                              c            ×            fd                                2            ⁢                          f              0                                                          (        6        )            
Wherein, c is the speed of light, T is a frequency sweep time, Fs is the bandwidth of sweep frequency and f0 is a frequency center of the transmitting signal.
However, it is complicate to process the reflecting wave of a plurality of the target. The radar in the prior art must completely scan upsweep frequency signal and downsweep frequency signal and then the relative frequency shift is got between the target and the radar. Hence, the relative frequency shift between the target and the radar causes the longer operation time in the prior art. Besides, the scan upsweep frequency signal and the downsweep frequency signal are adopted non-coherent integration process in whole detected area of the radar in the prior art, so the memory of the radar is consumed and the signal process efficiency is reduced.
Accordingly, the invention provides a target tracking method of radar with frequency modulated continuous wave, which detects the whole signals in a part of detected range. The target tracking method of radar with frequency modulated continuous wave only utilizes the upsweep frequency signal or the downsweep frequency signal to calculate the relative distance between the radar and the target and reduce the operation time of the radar. Then, the process efficiency of the radar is increased.